Hypertension, or high blood pressure, is the most common disease affecting the heart and blood vessels. Statistics indicate that hypertension occurs in more than 50 million Americans. The prevalence of hypertension increases with age. Between 85 and 90% of cases are primary (i.e., essential) hypertension, i.e., a persistently elevated blood pressure that cannot be attributed to any particular organic cause. The remaining percentage of cases are secondary hypertension, i.e., elevated blood pressure having an identifiable underlying cause such as kidney disease and adrenal hypersecretion.
Hypertension is of considerable concern because of the harm it can do to the heart, brain, and kidneys if it remains uncontrolled. The heart is most commonly affected by high blood pressure. When blood pressure is high, the heart uses more energy in pumping against the increased resistance caused by the elevated arterial blood pressure. Because of the increased effort, the heart muscle thickens and the heart becomes enlarged and needs more oxygen. If it cannot meet the demands put on it, angina pectoris or even myocardial infarction may develop. Hypertension can result in numerous complications include left ventricular failure; atherosclerotic heart disease; retinal hennorrhages, exudates, papilledema, and vascular accidents; cerebrovascular insufficiency with or without stroke; and renal failure. An untreated hypertensive patient is at great risk of developing disabling or fatal left ventricular failure, myocardial infarction, cerebral hemorrhage or infarction, or renal failure at early age. Hypertension is the most important risk factor predisposing to stroke and is an important risk factor predisposing to coronary atherosclerosis.
An abnormal blood pressure can also result from specific conditions or diseases, such as heart failure. Heart failure is a chronic or acute state that results when the heart is not capable of providing sufficient cardiac output to satisfy the metabolic needs of the body. Heart failure is commonly referred to as congestive heart failure (CHF), since symptoms of increased venous pressure (pulmonary congestion with left heart failure and peripheral edema with right heart failure) are often predominant. Symptoms and signs of CHF include fatigue, peripheral and pulmonary edema, and visceral congestion (e.g., dyspnea). These symptoms are produced by diminished blood flow to the various tissues of the body and by accumulation of excess blood in the various organs, that results from the heart being incapable of pumping out the blood. Heart failure can result from several underlying diseases, most commonly in industrialized nations from atherosclerotic coronary artery disease with myocardial infarction. Myocardidis, various cardiomyopathies, and valvular and congenital defects may also result in heart failure (Anderoli et al., Cecil: Essentials of Medicine, Third Edition, WB Saunders Company, 1993). A major problem in CHF is the inability of the failing left ventricle to maintain a normal blood pressure, thus resulting in increased pre- and afterload, and leading to progressive ventricular dilation with wall remodeling. Vasodilators which induce a reduction in pre- and afterload, i.e., reduction of the systemic vascular resistance and reduction of the peripheral vascular resistance, respectively, are currently used to treat CHF (Lionel H. Opie, Drugs for the Heart, Third Edition, WB Saunders Company, 1991).
One important system involved in regulating blood pressure is the renin-angiotensin-aldosterone system. In this system, renin, a proteolytic enzyme formed in the granules of the juxtaglomerular apparatus cells catalyzes the conversion of angiotensinogen (a plasma protein) into angiotensin 1, a decapeptide. This inactive product is then cleaved by a converting enzyme, termed angiotensin converting enzyme (ACE) mainly in the lung, but also in the kidney and brain, to an octapeptide, angiotensin II, which is a potent vasoconstrictor and also stimulates the release of aldosterone. Aldosterone is an adrenal cortex hormone that promotes the retention of salt and water by the kidneys and thus increases plasma volume, resulting in an increase in blood pressure. Angiotensin II also stimulates the release of norepinephrine from neural cells which interacts with specific receptors on blood vessels, thereby resulting in an increase in calcium and vasocontriction. Another mechanism by which angiotensin II induces vasoconstriction is by interacting with specific receptors on blood vessels, thereby resulting in an opening of calcium channels and an increase in calcium, resulting in vasoconstriction.
ACE, also referred to as peptidyl dipeptidase A (EC 3.4.15.1) and kininase II is a metallopeptidase, more particularly a zinc peptidase which hydrolyses angiotensin I and other biologically active polypeptides, such as kinins, e.g., bradykinin. Bradykinin is a vasodilator, which acts at least in part by inducing release of vasodilator prostaglandins, and which is inactivated upon hydrolysis by ACE. Thus, ACE increases blood pressure at least in part by producing angiotensin II, a vasoconstrictor, and by inactivating bradykinin, a vasodilator. Bradykinin is also involved in other biological activities including mediation of pain and inflammatory reactions.
The role of ACE in regulating blood pressure is further demonstrated at least by the efficacy of ACE inhibitors in reducing hypertension and treating CHF in individuals. ACE inhibitors have major roles as vasodilators in hypertension and CHF and are among the most efficient drugs for treating these disorders (see, e.g., Opie et al., Angiotensin Converting Enzyme Inhibitors and Conventional Vasodilators, in Lionel H. Opie, Drugs for the Heart, Third Edition, WB Saunders Company, 1991, p106). Several clinical trials indicate that ACE inhibitors prolong survival in a broad spectrum of patients with myocardial infarction and heart failure, ranging from those who are asymptomatic with ventricular dysfinction to those who have symptomatic heart failure but are normotensive and hemodynamically stable. For example, one study demonstrated a 40% reduction in mortality at 6 months in patients with severe heart failure (The CONSENSUS Trial Study Group, N. Engl. J. Med. 316:1429(1987); The CONSENSUS Trial Study Group, N. Engl. J. Med. 325:293(1991)).
ACE cleaves substrates other than angiotensin I and bradykinin. For example, ACE cleaves enkephalins, as well as heptapeptide and octapeptide enkephalin precursors. ACE also hydrolyzes the tridecapeptide neurotensin to a dipeptide and undecapeptide (Skidgel et al. In Neuropeptides and Their Peptidases, Ed. Turner A J, Chichester, U K, Ellis-Horwood, (1987)). ACE can also cleave and thereby inactivate substance P (Skidgel et al., supra).
Several ACE inhibitors are currently available on the market (e.g., Captopril, Enalapril, Fosinopril, Lisinopril, and Ramipril). However, ACE inhibitors in large doses can cause a variety of undesirable secondary effects including nephrotic syndrome, membraneous glomerulonephritis, nephritis, and leukopenia, as well as angioedema.
The isolation of novel nucleic acids encoding novel ACE proteins would be useful, e.g., in developing drugs which are capable of regulating the activity of ACE without having the negative secondary effects.
The present invention is based, at least in part, on the discovery of a novel gene encoding a novel human protein, having sequence homologies with known angiotensin converting enzymes (ACEs). Thus, the newly identified proteins and nucleic acids described herein are referred to as xe2x80x9cangiotensin converting enzyme-2xe2x80x9d or xe2x80x9cACE-2xe2x80x9d. The human ACE-2 gene transcript is shown in FIG. 1 (SEQ ID NO: 1) and includes 5xe2x80x2 and 3xe2x80x2 untranslated regions and a 2415 base pair open reading frame (SEQ ID NO: 3) encoding an 805 amino acid polypeptide having SEQ ID NO: 2. The mature protein, i.e., the full length protein without the signal sequence is comprised of about 787 amino acids. ACE-2 is expressed predominantly in kidney and testis. A nucleic acid comprising the cDNA encoding the full length human ACE-2 polypeptide has been deposited at the American Type Culture Collection (12301 Parklawn Drive, Rockville, Md.) on Dec. 3, 1997 has been assigned ATCC Designation No. 209510.
An amino acid and nucleotide sequence analysis using the BLAST program (Altschul et al. (1990) J. Mol. Biol. 215:403) revealed that certain portions of the amino acid and nucleic acid sequences of the newly identified human ACE-2 protein and nucleic acid have a sequence similarity with certain regions of angiotensin converting enzymes. In particular, the amino acid sequence of the zinc binding domain, which is conserved in all ACE proteins identified to date and which is located in the catalytic site of the enzyme and necessary for catalytic activity, is also found in ACE-2. Amino acids which have been identified as either contacting the zinc atom and/or involved in the catalysis and are conserved among all ACE proteins, are present in ACE-2. Thus, ACE-2 is believed to share at least some of the biological activities of ACE proteins, in particular the peptidase activity. In fact, as shown herein (see Example 5.4), ACE-2 cleaves the C-terminal amino acid from angiotensin I to produce Ang (1-9). ACE-2 also comprises a transmembrane domain which is present in most ACE proteins and which is likely to mediate protein attachment to the cell membrane. Except for the presence of other small regions of homology between ACE-2 and known ACE proteins, the other portions of ACE-2 are significantly different from those of known ACE proteins.
In one aspect, the invention features isolated ACE-2 nucleic acid molecules. In one embodiment, the ACE-2 nucleic acid is from a vertebrate. In a preferred embodiment, the ACE-2 nucleic acid is from a mammal, e.g. a human. In an even more preferred embodiment, the nucleic acid has the nucleic acid sequence set forth in SEQ ID NO:1 and/or 3 or a portion thereof. The disclosed molecules can be non-coding, (e.g. a probe, antisense, or ribozyme molecules) or can encode a functional ACE-2 polypeptide (e.g. a polypeptide which specifically modulates biological activity, by acting as either an agonist or antagonist of at least one bioactivity of the human ACE-2 polypeptide). In one embodiment, the nucleic acid molecules can hybridize to the ACE-2 gene contained in ATCC designation No. 209510. In another embodiment, the nucleic acids of the present invention can hybridize to a vertebrate ACE-2 gene or to the complement of a vertebrate ACE-2 gene. In a further embodiment, the claimed nucleic acid can hybridize with a nucleic acid sequence shown in FIG. 1. (SEQ ID NOs: 1 and 3) or complement thereof. In a preferred embodiment, the hybridization is conducted under mildly stringent or stringent conditions.
In further embodiments, the nucleic acid molecule is an ACE-2 nucleic acid that is at least about 70%, preferably about 80%, more preferably about 85%, and even more preferably at least about 90% or 95% homologous to the nucleic acid shown as SEQ ID NOs: 1 or 3 or to the complement of the nucleic acid shown as SEQ ID NOs: 1 or 3. In a further embodiment, the nucleic acid molecule is an ACE-2 nucleic acid that is at least about 70%, preferably at least about 80%, more preferably at least about 85% and even more preferably at least about 90% or 95% similar in sequence to the ACE-2 nucleic acid contained in ATCC designation No. 209510 or shown set forth in SEQ ID NOs: 1 and/or 3 or complement thereof.
The invention also provides probes and primers comprising substantially purified oligonucleotides, which correspond to a region of nucleotide sequence which hybridizes to at least about 6 at least about 10, and at least about 15, at least about 20, or preferably at least about 25 consecutive nucleotides of the sequence set forth as SEQ ID NO: 1 or complements of the sequence set forth as SEQ ID NO: 1 or naturally occurring mutants or allelic variants thereof, such as those described in the Examples. In preferred embodiments, the probe/primer further includes a label group attached thereto, which is capable of being detected.
For expression, the subject nucleic acids can be operably linked to a transcriptional regulatory sequence, e.g., at least one of a transcriptional promoter (e.g., for constitutive expression or inducible expression) or transcriptional enhancer sequence. Such regulatory sequences in conjunction with an ACE-2 nucleic acid molecule can provide a useful vector for gene expression. This invention also describes host cells transfected with said expression vector whether prokaryotic or eukaryotic and in vitro (e.g. cell culture) and in vivo (e.g. transgenic) methods for producing ACE-2 proteins by employing said expression vectors.
In another aspect, the invention features isolated ACE-2 polypeptides, preferably substantially pure preparations, e.g. of plasma purified or recombinantly produced polypeptides. The ACE-2 polypeptide can comprise a full length protein or can comprise smaller fragments corresponding to one or more particular motifs/domains, or fragments comprising at least about 5, 10, 25, 50, 75, 100, 125, 130, 135, 140 or 145 amino acids in length. In particularly preferred embodiments, the subject polypeptide has an ACE-2 bioactivity, for example, it is capable of interacting with and/or hydrolyzing a target peptide, such as angiotensin 1, kinetensin, bradykinin or neurotensin.
In a preferred embodiment, the polypeptide is encoded by a nucleic acid which hybridizes with the nucleic acid sequence represented in SEQ ID NOs: 1 and 3. In a further preferred embodiment, the ACE-2 polypeptide is comprised of the amino acid sequence set forth in SEQ ID NO: 2. The subject ACE-2 protein also includes within its scope modified proteins, e.g. proteins which are resistant to post-translational modification, for example, due to mutations which alter modification sites (such as tyrosine, threonine, serine or aspargine residues), or which prevent glycosylation of the protein, or which prevent interaction of the protein with intracellular proteins involved in signal transduction.
The ACE-2 polypeptides of the present invention can be glycosylated, or conversely, by choice of the expression system or by modification of the protein sequence to preclude glycosylation, reduced carbohydrate analogs can also be provided. Glycosylated forms can be obtained based on derivatization with glycosaminoglycan chains. Also, ACE-2 polypeptides can be generated which lack an endogenous signal sequence (though this is typically cleaved off even if present in the pro-form of the protein).
In yet another preferred embodiment, the invention features a purified or recombinant polypeptide, which has the ability to modulate, e.g., mimic or antagonize, an activity of a wild-type ACE-2 protein, e.g., its ability to bind and/or hydrolyze angiotensin I, kinetensin, bradykinin, or neurotensin, or a peptide having a significant amino acid homology thereto. Preferably, the polypeptide comprises an amino acid sequence identical or homologous to a sequence designated in SEQ ID No: 2.
Another aspect of the invention features chimeric molecules (e.g., fusion proteins) comprising an ACE-2 protein. For instance, the ACE-2 protein can be provided as a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated (heterologous) to the ACE-2 polypeptide. A preferred ACE-2 fusion protein is an immunoglobulin-ACE-2 fusion protein, in which an immunoglobulin constant region is fused to an ACE-2 polypeptide.
Yet another aspect of the present invention concerns an immunogen comprising an ACE-2 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for an ACE-2 polypeptide; e.g. a humoral response, an antibody response and/or cellular response. In a preferred embodiment, the immunogen comprises an antigenic determinant, e.g. a unique determinant of a protein encoded by the nucleic acid set forth in SEQ ID NO: 1 or 3; or as set forth in SEQ ID NO:2.
A still further aspect of the present invention features antibodies and antibody preparations specifically reactive with an epitope of an ACE-2 protein.
The invention also features transgenic non-human animals-which include (and preferably express) a heterologous form of an ACE-2 gene described herein, or which misexpress an endogenous ACE-2 gene (e.g., an animal in which expression of one or more of the subject ACE-2 proteins is disrupted). Such transgenic animals can serve as animal models for studying cellular and/or tissue disorders comprising mutated or mis-expressed ACE-2 alleles or for use in drug screening. Alternatively, such transgenic animals can be useful for expressing recombinant ACE-2 polypeptides.
The invention further features assays and kits for determining whether an individual""s ACE-2 genes and/or proteins are defective or deficient (e.g in activity and/or level), and/or for determining the identity of ACE-2 alleles. In one embodiment, the method comprises the step of determining the level of ACE-2 protein, the level ACE-2 mRNA and/or the transcription rate of an ACE-2 gene. In another preferred embodiment, the method comprises detecting, in a tissue of the subject, the presence or absence of a genetic alteration, which is characterized by at least one of the following: a deletion of one or more nucleotides from a gene; an addition of one or more nucleotides to the gene; a substitution of one or more nucleotides of the gene; a gross chromosomal rearrangement of the gene; an alteration in the level of a messenger RNA transcript of the gene; the presence of a non-wild type splicing pattern of a messenger RNA transcript of the gene; and/or a non-wild type level of the ACE-2 protein.
For example, detecting a genetic alteration or the presence of a specific polymorphic region can include (i) providing a probe/primer comprised of an oligonucleotide which hybridizes to a sense or antisense sequence of an ACE-2 gene or naturally occurring mutants thereof, or 5xe2x80x2 or 3xe2x80x2 flanking sequences naturally associated with the ACE-2 gene; (ii) contacting the probe/primer with an appropriate nucleic acid containing sample; and (iii) detecting, by hybridization of the probe/primer to the nucleic acid, the presence or absence of the genetic alteration. Particularly preferred embodiments comprise: 1) sequencing at least a portion of an ACE-2 gene, 2) performing a single strand conformation polymorphism (SSCP) analysis to detect differences in electrophoretic mobility between mutant and wild-type nucleic acids; and 3) detecting or quantitating the level of an ACE-2 protein in an immunoassay using an antibody which is specifically immunoreactive with a wild-type or mutated ACE-2 protein.
Information obtained using the diagnostic assays described herein (alone or in conjunction with information on another genetic defect, which contributes to the same disease) is useful for diagnosing or confirming that a symptomatic subject (e.g. a subject symptomatic for hypertension, hypotension, CHF, or a kinetensin-associated condition), has a genetic defect (e.g. in an ACE-2 gene or in a gene that regulates the expression of an ACE-2 gene), which causes or contributes to the particular disease or disorder. Alternatively, the information (alone or in conjunction with information on another genetic defect, which contributes to the same disease) can be used prognostically for predicting whether a non-symptomatic subject is likely to develop a disease or condition, which is caused by or contributed to by an abnormal ACE-2 activity or protein level (e.g. hypertension, hypotension, CHF, or a kinetensin-associated condition) in a subject. In particular, the assays permit to ascertain an individual""s predilection to develop a condition associated with a mutation in ACE-2, where the mutation is a single nucleotide polymorphism (SNP). Based on the prognostic information, a doctor can recommend a regimen (e.g. diet or exercise) or therapeutic protocol useful for preventing or prolonging onset of the particular disease or condition in the individual.
In addition, knowledge of the particular alteration or alterations, resulting in defective or deficient ACE-2 genes or proteins in an individual, alone or in conjunction with information on other genetic defects contributing to the same disease (the genetic profile of the particular disease) allows customization of therapy for a particular disease to the individual""s genetic profile, the goal of xe2x80x9cpharmacogenomicsxe2x80x9d. For example, an individual""s ACE-2 genetic profile or the genetic profile of a disease or condition, to which ACE-2 genetic alterations cause or contribute, can enable a doctor: 1) to more effectively prescribe a drug that will address the molecular basis of the disease or condition; and 2) to better determine the appropriate dosage of a particular drug. For example, the expression level of ACE-2 proteins, alone or in conjunction with the expression level of other genes, known to contribute to the same disease, can be measured in many patients at various stages of the disease to generate a transcriptional or expression profile of the disease. Expression patterns of individual patients can then be compared to the expression profile of the disease to determine the appropriate drug and dose to administer to the patient.
The ability to target populations expected to show the highest clinical benefit, based on the ACE-2 or disease genetic profile, can enable: 1) the repositioning of marketed drugs with disappointing market results; 2) the rescue of drug candidates whose clinical development has been discontinued as a result of safety or efficacy limitations, which are patient subgroup-specific; and 3) an accelerated and less costly development for drug candidates and more optimal drug labeling (e.g. since the use of ACE-2 as a marker is useful for optimizing effective dose).
In another aspect, the invention provides methods for identifying a compound which modulates an ACE-2 activity, e.g. the interaction between an ACE-2 polypeptide and a target peptide, e.g., angiotensin I, a kilin, kinetensin or neurotensin. In a preferred embodiment, the method includes the steps of (a) forming a reaction mixture including: (i) an ACE-2 polypeptide, (ii) an ACE-2 binding partner (e.g., a target peptide, such as angiotensin I or kinetensin), and (iii) a test compound: and (b) detecting interaction of the ACE-2 polypeptide and the ACE-2 binding protein. A statistically significant change (potentiation or inhibition) in the interaction of the ACE-2 polypeptide and ACE-2 binding protein in the presence of the test compound, relative to the interaction in the absence of the test compound, indicates a potential agonist (mimetic or potentiator) or antagonist (inhibitor) of ACE-2 bioactivity for the test compound. The reaction mixture can be a cell-free protein preparation, e.g., a reconstituted protein mixture or a cell lysate, or it can be a recombinant cell including a heterologous nucleic acid recombinantly expressing the ACE-2 binding partner.
In preferred embodiments, the step of detecting interaction of the ACE-2 and ACE-2 binding partner (e.g., angiotensin I or kinetensin) is a competitive binding assay.
In preferred embodiments, at least one of the ACE-2 polypeptide and the ACE-2 binding partner comprises a detectable label, and interaction of the ACE-2 and ACE-2 binding partner is quantified by detecting the label in the complex. The detectable label can be, e.g., a radioisotope, a fluorescent compound, an enzyme, or an enzyme co-factor. In other embodiments, the complex is detected by an immunoassay.
The invention also provides a methods for identifying an ACE-2 therapeutic, comprising contacting in a reaction mixture an ACE-2 polypeptide, a target peptide or analog thereof or portion thereof, and a test compound, in conditions wherein, but for the presence of the test compound, the ACE-2 polypeptide cleaves one or more amino acids from the target peptide or analog thereof or portion thereof to produce an ACE-2 target pcptide conversion product, and detecting the presence of at least one of the target peptide or analog thereof or portion thereof, the ACE-2 target peptide conversion product, and one or more amino acids. A preferred method for determining the presence and/or the amount of at least one of the target peptide or analog thereof or portion thereof, the ACE-2 target peptide conversion product, and one or more amino acids comprises obtaining a mass spectrum of the reaction mixture or of a part thereof.
Yet another exemplary embodiment provides an assay for screening test compounds to identify agents which modulate the amount of ACE-2 produced by a cell. In one embodiment, the screening assay comprises contacting a cell transfected with a reporter gene operably linked to an ACE-2 promoter with a test compound and determining the level of expression of the reporter gene. The reporter gene can encode, e.g., a gene product that gives rise to a detectable signal such as: color, fluorescence, lurninescence, cell viability, relief of a cell nutritional requirement, cell growth, and drug resistance. For example, the reporter gene can encode a gene product selected from the group consisting of chloramphenicol acetyl transferase, luciferase, beta-galactosidase and alkaline phosphatase.
Also within the scope of the invention are methods for treating diseases or disorders which are associated with an aberrant ACE-2 level or activity or which can benefit from modulation of the activity or level of ACE-2, in particular diseases or conditions which are improved by modulation of the level of one or more angiotensin I conversion products, e.g., by an increase or decrease in the production of Ang.(1-9), Ang.(1-5), and/or Ang.(1-8) (angiotensin II); conditions that are improved by modulation of kinetensin or kinetensin (1-8) level; conditions that are improved by modulation of bradykinin (1-8) or bradykinin (1-7); or conditions that are improved by modulation of neurotensin (1-13) or neurotensin (1-12). Thus, the invention provides methods for treating hypertension, CHF, inflammatory reactions, allergic reactions, and methods to reduce pain. The methods comprise administering, e.g., either locally or systemically to a subject, a pharmaceutically effective amount of a composition comprising an ACE-2 therapeutic. Depending on the condition, the therapeutic can be an ACE-2 agonist or an ACE-2 antagonist. For example, an ACE-2 antagonist therapeutic can be administered to a subject having hypertension or CHF. In another embodiment, an ACE agonist is administered locally to a subject to reduce the inflammation and pain resulting from an insect sting or bite, which was accompanied by an injection of bradykinin.
In a particular embodiment of the invention, an ACE-2 antagonist is administered to a subject alone or together with an ACE antagonist. Thus, a dual therapy comprising administering to a subject an antagonist of ACE-2 and an antagonist of ACE can be used to prevent the accumulation of angiotensin II, e.g., to thereby reduce the blood pressure of the subject and prevent the development or appearance of conditions related thereto.
The invention also provides methods for identifying other potential substrates of an ACE-2 polypeptide as well as the product of the enzymatic reaction. In a preferred embodiment, the method comprises contacting a preparation containing an ACE-2 polypeptide with a test compound, e.g., a peptide, for a time sufficient for the enzymatic reaction to occur, and subjecting the reaction mixture, or a portion thereof, to mass spectrometry. The comparison of the mass spectra of the test compound with that of the reaction mixture after incubation to allow the enzymatic reaction to occur, will indicate whether the test compound was converted into a new compound, in which case the test compound is a substrate of the ACE-2 polypeptide.
Other features and advantages of the invention will be apparent from the following detailed description and claims.